California business owners and nonresident investors face complex rules involving income sourcing, nexus, partnerships, S corporations, and business sales. This updated guide explains California multistate taxation and the important 2026 OTA decision rejecting the FTB's Section 751(a) partnership interest sourcing position.

A missed or underpaid June 15 payment no longer automatically eliminates the 2026 California PTE election. Learn how the 12.5% owner credit reduction is calculated, when the election may still produce federal tax savings, and how to prepare for the 2027 deadline.